1. Field of the Invention
The present invention relates to gaseous display and/or memory systems. More particularly, the present invention relates to plasma gas discharge cells and arrays thereof. Still more particularly, the present invention relates to such cells and arrays disposed on a single substrate.
2. Description of the Prior Art
The subject of gaseous display and memory systems has recently received considerable attention. Such systems utilizing the glow discharge phenomenon resulting from the application of electric fields to one or more inert gases possesses negative impedance characteristics and, therefore, inherent memory. Thus, rather than requiring constant refreshing by a separate source of signals it is sufficient for such gaseous display systems to have applied to them an initial set of signals defining a desired on/off pattern. Maintenance of the resulting glows is achieved by the application of a non-information-bearing sustain signal sequence of lesser magnitude than those signals used to write the information in the first instance.
A typical configuration for such gaseous display/memory systems assumes the form of a so-called plasma discharge panel of the type described, for example, in U.S. Pat. No. 3,559,190 issued Jan. 26, 1971 to D. L. Bitzer et al. The basic structure of a plasma panel in accordance with the teachings of Bitzer et al. includes a "sandwich" of three dielectric layers, the outermost ones of which have mutually orthogonal sets of conductors plated or otherwise laid upon the exterior surface thereof. The intermediate dielectric layer typically has a plurality of perforations therein, with one perforation appearing at the "intersection" of the conductors on the exterior dielectric layers. Thus when the three layers are brought together in typical embodiment there is formed a cavity containing neon, argon, or some other inert gas (or some combination thereof) in which a glow discharge formed by potential differences created on the exterior conductors may be maintained.
Since the discharge is formed between the sets of conductors, it is necessary, if any useful light is to appear on the exterior of the sandwich, that the conductors be transparent to some substantial degree. As might be expected, however, in practice a significant portion of the light actually generated is absorbed by the conducting electrodes.
It is, therefore, an object of the present invention to provide a plasma discharge panel wherein little or no light is masked by the driving electrodes.
Another obvious characteristic of the Bitzer et al display panel is that the outer layers of the three layer sandwich must be maintained in constant spaced-apart relation in order to maintain uniform discharge characteristics over a matrix of many conductor intersections or cells. While the intermediate dielectric layer having perforations therein serves to provide some degree of constancy with respect to the separation of the exterior layers, nevertheless it introduces other alignment problems requiring that the perforations be lined up with considerable exactitude with respect to the intersection of conductors. Other spacing means have been used from time to time to maintain a uniform spacing between the conductor-bearing dielectric layers. Thus, for example, individual dielectric spheres of the correct diameter have been used in some cases to provide the proper spacing. In actual manufacture, however, some degree of compression of the spheres in a position-dependent manner occurs. Other efforts utilizing spacers of the form of fiber optic tubes have met with similar disadvantages and resulting lack of uniformity of spacing.
It is, therefore, an object of the present invention to eliminate the need for spacers defining a gas-filled cavity between conductors for purposes of developing a uniform glow discharge at cells disposed on a two-dimensional panel.
In U.S. Pat. No. 3,603,836 issued Sept. 7, 1971 to J. D. Grier, an alternative panel structure is provided in which electrodes on each of the exterior layers of a panel sandwich are bifurcated to, in effect, generate a discharge which is not wholly obscured by the conductors. In typical operation the Grier panel causes a discharge to occur under the space between each of the bifurcated portions of a conductor path. The Grier systems, however, requires that the conductor-bearing layers be maintained in constant spaced-apart relation, thereby sharing the difficulty in fabrication with the Bitzer et al. system.
U.S. Pat. No. 3,602,756 issued Aug. 31, 1971 to R. E. Bonnet describes a plasma panel which comprises a woven wires mesh of non-electrically contacting intersecting wires in place of conductors disposed on planes having constant separation. Again, fabrication difficulties can arise in such systems by virtue of the required "weaving" operations. Thus the process does not lend itself to such modern fabrication techniques as thin or thick film deposition on planar substrates. Also, because the Bonnet structure is not planar, it may prove difficult to introduce isolating structures intermediate the individual cells or crosspoints. Thus to avoid spurious ignition of one cell, it may be necessary to separate it from an adjacent ignited cell by a considerable physical difference. High resolution displays are therefore more difficult to realize using the Bonnet system.
U.S. Pat. No. 3,646,384 issued Feb. 29, 1972 to F. M. Lay describes a so-called "one-sided plasma display panel." The panel shown three points out many of the difficulties enumerated above for the three-layer sandwich panels relating to spacing and the like. However, the structure proposed by Lay, which basically involves the plating on both sides of an insulating sheet, the whole then being enclosed within a neon atmosphere, was used with electrode spacing of one-third of an inch. Such spacing is, of course, not appropriate for use in panels requiring high crosspoint density, i.e., high resolution. In subsequent U.S. Pat. No. 3,719,940 issued Mar. 6, 1973, Lay describes an improvement to panels of the "one-sided" type. However, the improvements made relate to techniques for preventing firing or sustaining of unselected cells during addressing operations, which improvements relate to altering the drive pulse sequencing of a panel of the type described in U.S. Pat. No. 3,666,981 also issued to Lay on May 30, 1972. This latter patent describes a panel with a grid network of conductors intermediate the drive electrodes for purposes of enhancing the shielding therebetween.
It is therefore an object of the present invention to provide a "one-sided" or single-substrate plasma panel structure which permits the realization of high cell density.